1. Field of the Invention
The present invention relates to an optical semi-conductor module for use, for example, in an optical communication system.
2. Description of the Prior Art
FIG. 2 is a sectional view of a typical coventional optical semiconductor module.
Referring to the figure, reference numeral 1 denotes a receptacle, and 2 an external thread which is provided on the receptacle 1. The external thread 2 is engaged with an internal thread 5 which is provided in a connecting nut 4 that constitutes an optical connector plug 3. The receptacle 1 is provided with a bore 6 along the central axis thereof for insertion of a ferrule 8 that retains an optical fiber 7. The receptacle 1 has a wall 9 that limits the depth to which the ferrule 8 is inserted, and further has a light passing bore 10. A rod lens 11 inserted into a bore 12 that is provided in the receptacle 1, and secured by means of a screw 13. A holder 14 has an optical semiconductor element 15 secured thereto by means, for example, of bonding. The holder 14 is secured to the receptacle 1 at a junction plane 16 by means, for example, of welding. It should be noted that when the rod lens 11 and the holder 14 are fixed, the position of the rod lens 11 must be adjusted in the same direction as the optical axis of the optical fiber 7, and the position of the holder 14 must be adjusted in a direction perpendicular to the optical axis of the optical fiber 7. The positional adjustment is effected by varying the degree to which the screw 13 is tightened.
The operation of the prior art will next be expained. The ferrule 8 is inserted into the bore 6, and the internal thread 5 is coupled with the external thread 2, thereby fitting the optical connector plug 3 to the receptacle 1. Thus, light that is emitted from the optical semiconductor element 15 is condensed through the rod lens 11 to enter the optical fiber 7 that is retained in the ferrule 8, thereby achieving optical coupling.
The conventional optical semiconductor module having the above-described arrangement suffers, however, from the following problems:
In adjustment of the position of the rod lens 11 in the same direction as the optical axis of the optical fiber 7, every time the rod lens 11 is moved by a very small amount for adjustment, it is necessary to remove the receptacle 1 from a fixing jig for assembly and retighten the screw 3. Thus, the prior art is inferior in terms of operating efficiency.
It is particularly difficult to align the respective optical axes of the optical semiconductor element 15 and the rod lens 11, and an angular displacement is very likely to occur in the process of securing the holder 14 to the receptacle 1. If an angulr displacement occurs, it is amplified through the rod lens 11. Accordingly, even if the angular displacement is very small, the light output from the rod lens 11 deviates by a large margin from the optical axis of the optical fiber 7. In consequence, the desired performance cannot be consistently obtained.